The movement depends on the type of joints which join two bones together. The body parts having ball and socket joint move in all directions while the body parts having hinge joint move only in one direction.

Elbow is not one long bone from the upper arm to our wrist. It is different bones joined together at the elbow. The joint present at the elbow is hinge joint that helps in its bending.

The bodies of insects, crabs, spiders have  hard covering made up of chitin. These animals do not have endoskeleton.
Instead, this hard covering gives them a shape, so it is called exoskeleton. Scales of fishes and cockroaches, outer shells of snail and oyster are also examples of exoskeleton

The difference between bone and cartilage

The doctor must have observed a swelling around his ankle and taken an X-ray of his ankle. X-ray images confirm any type of injuries/fractures in the bones.

Cockroaches walk and climb as well as fly in the air. They have three pairs of legs which help them in walking. The body is covered with a hard outer skeleton. This outer skeleton is made of different units joined together which permit movement. There are two pairs of wings attached to the thorax. The cockroaches have distinct muscles-those near the legs move the legs for walking. The thoracic muscles move the wings when the cockroach flies.

The framework of bones and cartilage which supports the body of an animal is called its skeletal system.
Human skeletal system is made up of 206 bones and cartilage. The human skeletal system consists of the skull, backbone, ribs, breastbone, bones in arms and legs, shoulder and hip bones.
Functions of the skeletal system:
(i) It forms framework of the body.
(ii) It helps to protect the delicate organs of the body in their proper positions.

(a) The doctor has diagnosed the fracture by taking photographs of bones, i.e. X-ray images.
(b) X-rays show us the images and shapes of different bones in our body.
(c) Friendly behaviour, sense of responsibility and kind nature are the values shown by Rishi's friends.

The skeleton of a bird is well-suited for flying because
(i) bones are hollow and light in weight
(ii) bones of hindlimbs are used for walking and perching.
(iii) bones of forelimbs are modified as wings.
(iv) shoulder bones are strong, thus helpful in flying.
(v) breast bones hold flight muscles and are used to move the wings up and down for flying.

A snake form loops in its body while slithering. Each loop of the snake gives it a forward push by pressing against the ground. The snake with a larger number of loops will move much faster than the snake with lesser number of loops. Thus, the snake A will move faster than snake B as we can see that loops in snake A are more than in snake B.